Use of elastic to improve the fit of reusable garments or to provide a seal at desirable locations in reusable garments is well known. Elastic in such garments is typically sewn in or confined between garment layers in either an elongated or relaxed condition. In most cases, the elastic is affixed on an individual garment by garment basis.
In disposable garments, such as disposable diapers, methods and apparatus have been developed to apply elastic ribbon at high fabricating speeds by use of an adhesive to bond the elastic ribbon to a continuous web. The web and elastic ribbon composite is subsequently cut into individual pieces for final use as elements of finished disposable garments. Because of the need for high speed and the consequent complexities of applying elastic to a web, the elastic is usually applied along a straight line. Typical arrangements for applying elastic along a straight line to a web are those shown in Buell U.S. Pat. No. 4,081,301 and Sabee U.S. Pat. No. 4,227,952. In the case of the Buell patent, the elastic and web substrate are continuously run at high speed while adhesive is intermittently applied to the elastic. The elastic and web are then brought together so that the elastic is adhered to the web at spaced apart locations. The web and elastic are then cut transversely at approximately the midpoint locations of the unadhered elastic to provide separate members for use in completing a disposable diaper. The arrangement used by Sabee entails the folding of the web substrate and the continuous application of adhesive to the elastic ribbon. The web and ribbon are then brought together and adhered to each other, except at the folded portions of the web. The elastic is then opposite the folded portions and the web is straightened. The result is a continuous web having straight elastic only in what will be the leg portions of a disposable diaper. The continuous web is then cut transversely midway between the ends of adjacent elastic strips to form separate sections for use in fabricating finished disposable diapers.
Although elastic that is straight relative to a curved portion of the body along which the disposable garment is to fit provides a better fit than if no elastic is used, considerably better results can be obtained if the elastic can be curved or contoured to follow the body curvature, for example, the curvature of the thigh and crotch area of an infant when the diaper is being worn. Although some work has been done in this area, to the inventors' knowledge, very little of the results of this work is of any practical importance. One example of a prior art approach for applying curved elastic to a disposable garment is illustrated in Bourgeois U.S. Pat. No. 3,828,367. In Bourgeois, a pair of elastic ribbons are fed to curved grooves in a roll under which a continuous web passes. As the roll with the ribbons in its grooves goes over the web the ribbons are transferred in the contoured pattern of the grooves to the roll. One problem with a grooved roll for applying elastic ribbon to a web is that a groove which is sufficiently deep to guide the ribbon is too deep to apply a flat elastic ribbon. Usually, because of the better distribution of stress in a flat tensioned ribbon, a flat ribbon is preferred in garment elasticization applications. Also, a curved groove is unreliable insofar as preventing roping and C-folding of a flat ribbon is concerned.
It is a principle object of this invention to provide a method and apparatus for undulating or curving elastic ribbon while it is continuously moving and being applied to a continuously moving web. It is a further object to accomplish the aforesaid attachment of the elastic ribbon to a web along an undulated path in a relatively simple and accurate manner.